FIG. 1 shows a diagram of a drilling operation, in which a drilling rig (100) is used to turn a drill bit (150) coupled at the distal end of a drill pipe (140) in a borehole (145). The drilling operation may be used to obtain oil, natural gas, water, or any other type of material obtainable through drilling. Although the drilling operation shown in FIG. 1 is for drilling directly into an earth formation, those skilled in the art will appreciate that other types of drilling operations also exist, such as lake drilling or deep sea drilling.
As shown in FIG. 1, rotational power generated by a rotary table (125) is transmitted from the drilling rig (100) to the drill bit (150) via the drill pipe (140). Further, drilling fluid (also referred to as “mud”) is transmitted through the drill pipe's (140) hollow core to the drill bit (150). Specifically, a mud pump (180) is used to transmit the mud through a stand pipe (160), hose (155), and kelly (120) into the drill pipe (140). To reduce the possibility of a blowout, a blowout preventer (130) may be used to control fluid pressure within the borehole (145). Further, the borehole (145) may be reinforced using a casing (135), to prevent collapse due to a blowout or other forces operating on the borehole (145). The drilling rig (100) may also include a crown block (105), traveling block (110), swivel (115), and other components not shown.
Mud returning to the surface from the borehole (145) is directed to mud treatment equipment via a mud return line (165). For example, the mud may be directed to a shaker (170) configured to remove drilled solids from the mud. The removed solids are transferred to a reserve pit (175), while the mud is deposited in a mud pit (190). The mud pump (180) pumps the filtered mud from the mud pit (190) via a mud suction line (185), and re-injects the filtered mud into the drilling rig (100). Those skilled in the art will appreciate that other mud treatment devices may also be used, such as a degasser, desander, desilter, centrifuge, and mixing hopper. Further, the drilling operation may include other types of drilling components used for tasks such as fluid engineering, drilling simulation, pressure control, wellbore cleanup, and waste management.
In a given drilling operation (e.g., the drilling operation shown in FIG. 1), knowledge about the geomechanical properties of formations may be used to mitigate various drilling-related challenges. For example, some formations may present a risk of rock deformation or failure. Plasticity parameters are typically measured directly using mechanical tests performed on cores, while brittle-elastic properties may be predicted using mathematical correlations.
For example, methods for estimating the static Young's modulus are described in: Eissa, E. A. & Kazi, A. (1988) Relation between static and dynamic Young's moduli for rocks. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. 25, 479-482; Montmayour, H. & Graves, R. M. (1986) Prediction of Static Elastic/Mechanical Properties of Consolidated and Unconsolidated Sands From Acoustic Measurements: Correlations. 61st Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, New Orleans, La. SPE 15644; Morales, R. H. & Marcinew, R. P. (1993) Fracturing of high-permeability formations: Mechanical properties correlations. SPE 26561; Yale, D. P. & Jamieson, W. H. (1994) Static and Dynamic Rock Mechanical Properties in the Hugoton and Panoma Fields, Kansas. SPE Mid-Continent Gas Symposium, Amarillo, Tex., SPE 27939; and Tutuncu, A. N. & Sharma, M. M. (1992) Relating Static and Ultrasonic Laboratory Measurements to Acoustic Log Measurements in Tight Gas Sands. 67th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Washington, D.C., SPE 24689.
Further, methods for estimating the static Poisson's ratio from the dynamic Poisson's ratio are described in: Tutuncu & Sharma (1992) (referenced above); and Yale & Jamieson (1994) (referenced above). An empirical correlation for evaluating the Biot's constant is described in Krief, M., Garat, J., Stellingwerff J., & Ventre, J. (1990) A petrophysical interpretation using the velocities of P and S waves (full-waveform sonic). The Log Analyst 31, November, 355-369.
Moreover, correlations for estimating the unconfined compressive strength of rocks have been devised by several authors and are reviewed in Chang, C. (2004) Empirical Rock Strength Logging in Boreholes Penetrating Sedimentary Formations. MULLI-TAMSA (Geophysical Exploration) 7, 174-183. Additional correlations for this purpose are described in: Plumb, R. A., Herron S. L. & Olsen, M. P. (1992) Influence of Composition and Texture on Compressive Strength Variations in the Travis Peak Formation. 67th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Washington, D.C. SPE 24758; and Qiu, K., Marsden, J. R., Solovyov, Y., Safdar, M. & Chardac, O. (2005) Downscaling Geomechanics Data for Thin Bed Using Petrophysical Techniques. 14th SPE Middle East Oil and Gas Show and Conference, Bahrain. SPE 93605.